JP2007112933A - Resin composition for foam molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a molding having uniform and fine foamed cells by dispersing a powdery inorganic blowing agent into a similarly powdery carrier resin without melting and kneading the resin in order to uniformly disperse a blowing agent into a thermoplastic resin. <P>SOLUTION: An inorganic blowing agent such as a carbonate having 0.001-0.1mm average particle diameter in an amount of 0.1-50 pts.wt. is mixed with and dispersed into 100 pts.wt. of a thermoplastic resin having 0.01-1.0mm average particle diameter without melting the thermoplastic resin and is used for molding. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a foam molding resin composition for the purpose of uniformly dispersing an inorganic foaming agent having a foaming start temperature of about 150 ° C. or less as a foaming agent in a thermoplastic resin without melting and kneading the thermoplastic resin. It is characterized by providing.

Making foamed molded products by adding foaming agents such as inorganic carbonates to thermoplastic resins such as polypropylene and polystyrene resins makes it possible to reduce the weight of molded products, reduce material costs, and reduce the silencing properties and texture of molded products. It is applied to various molded products for the purpose of improvement.
Among these, it is a well-known fact that inorganic carbonates have been used universally from the past due to their harmless foaming residue and low cost. In addition, thermoplastic resins, especially polypropylene, have many features such as low specific gravity, good chemical resistance, low cost, and good moldability. Containers, sheets, trays, pipes Widely used in various molded products such as

  However, when the foaming agent is mainly composed of sodium hydrogen carbonate, which is generally used as an inorganic carbonate foaming agent, the foaming agent is melt-kneaded in advance in polypropylene and uniformly and finely dispersed can be used as an extruder, etc. It is not preferable because foaming has already started during the melting of polypropylene in the kneader.

  A method of dry blending a foaming agent into polypropylene pellets and subjecting it to foam molding is also described in Patent Document 1, but this method makes it difficult to uniformly disperse the foaming agent in the pellet resin. The expansion ratio differs between shots, and in extrusion molding, the expansion ratio and surface properties may vary over time, and this is not always an effective method.

  Further, as can be seen in Patent Document 2, it is also conceivable that when foaming a high melting point resin such as polyethylene terephthalate, a foaming agent of a different low melting point resin is previously kneaded to a high concentration and mixed during molding to be used for foam molding. However, by applying this method, for example, a master batch in which low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer is used as a base resin, and a foaming agent is melt-kneaded at a high concentration at low temperature. The molded product obtained by the method of creating and mixing with polypropylene resin at the time of molding and then subjecting to foam molding may deteriorate the excellent rigidity and heat resistance inherent to polypropylene, and the foam cell is not necessarily It is not always uniform and it is hard to say that it is a satisfactory work.

JP 2000-154270 A JP 2000-219782 A

  In the present invention, when preparing a resin composition to be subjected to foam molding, the foaming agent is heated to a powdery thermoplastic resin in order to disperse the foaming agent uniformly and finely in the thermoplastic resin regardless of melt kneading. And a resin composition in which the foaming agent is uniformly and finely dispersed on the surface of the powdered resin.

  The present invention relates to an inorganic foaming agent having an average particle diameter of 001 to 0.1 mm and 0.1 to 50 parts by weight of a thermoplastic resin with respect to 100 parts by weight of a thermoplastic resin having an average particle diameter of 0.01 to 1.0 mm. It is related with the resin composition for foam molding formed by disperse-mixing without melting.

  Furthermore, this invention relates to the said resin composition for foam molding whose inorganic foaming agent is carbonate.

  Furthermore, the present invention relates to a foam molded article obtained by blending the above resin composition into a thermoplastic resin and melt-molding it.

  The present invention uses an inorganic foaming agent as a foaming agent, preferably an inorganic carbonate, more preferably a powdered material mainly composed of sodium hydrogen carbonate, and further uses a powdered thermoplastic resin as a carrier resin. By uniformly and finely dispersing the foaming agent on the surface of the carrier resin without melting, uniform and fine foam cells can be stably formed during foam molding.

  As the thermoplastic resin as the carrier resin used in the present invention, all those generally used are applicable as long as the melt flow rate can be measured according to JIS K7210. Among them, all thermoplastic resin powders having a molding temperature of 150 or more are suitable. Specifically, polyvinyl chloride, low density polyethylene (including α-olefin copolymer), high density polyethylene, polypropylene, polystyrene, AS resin, ABS resin, polyamide and carboxylic acid or ester copolymer thereof, thermoplastic elastomer Etc. are also included.

The foaming agent used in the present invention may be any inorganic foaming agent that has been used universally.
More preferred is a foaming agent mainly composed of an inorganic carbonate, specifically sodium hydrogen carbonate. Sodium hydrogen carbonate is a substance originally used for medical use and food, and is widely used for foaming because of its high safety and low price. However, a disadvantage is that the foaming start temperature is slightly lower than other chemical foaming agents, for example, azodicarboxamide (ADCA) type foaming agents which are organic foaming agents having an azo bond.

  Therefore, it is also effective to improve the foaming start temperature by adding sodium hydrogen carbonate and an organic acid such as citric acid.

  The average particle diameter of the thermoplastic resin is preferably 0.01 to 1.0 mm. The reason for this is that when the average particle size is less than 0.1 mm, the bulk density of the thermoplastic resin decreases, the supply to the molding machine melting section during foam molding decreases, and dust scattering during handling at the beginning of weighing When the existing pellet resin is pulverized and used as the raw material, it takes time to pulverize, leading to an increase in cost.

  In addition, if the average particle diameter of the thermoplastic resin exceeds 1.0 mm, the surface area becomes small, so that the powdered foaming agent cannot be sufficiently adhered and dispersed on the resin surface, resulting in separation of excess foaming agent. This is not preferable because the foaming agent drops off and the concentration of the foaming agent in the material becomes uneven, making it difficult to perform uniform foam molding.

  The average particle diameter of the foaming agent is preferably 0.001 to 0.1 mm. The reason for this is that when the average particle diameter is less than 0.001 mm, the specific surface area of the foaming agent increases, and the foaming agent that does not adhere to the surface of the powdered carrier resin separates and falls off, resulting in uneven concentration of the foaming agent in the material. Therefore, it is difficult to perform uniform foam molding, which is not preferable.

  In addition, when the average particle diameter of the foaming agent exceeds 0.1 mm, the foaming agent particles once adhered and dispersed on the surface of the carrier resin are easily separated and dropped by vibration during operation, and the foaming agent in the material Since density unevenness occurs, it is difficult to perform uniform foam molding, which is not preferable.

  In the present invention, the average particle diameter of the thermoplastic resin and the average particle diameter of the inorganic foaming agent are those measured by a laser diffraction scattering method.

  The ratio of the foaming agent added to the carrier resin varies depending on the desired expansion ratio, molding temperature, resin type, and molding method, but is preferably 0.1 to 50 parts by weight with respect to 100 parts by weight of the carrier resin.

  If the amount of the foaming agent added is less than 0.1 parts by weight, a sufficient foaming ratio cannot be obtained, and the effect of adding the foaming agent cannot be seen. On the other hand, when the amount exceeds 50 parts by weight, it is difficult to perform uniform foam molding because the foaming agent in which the foaming agent particles do not completely adhere to the carrier resin particles is separated and dropped, resulting in uneven concentration of the foaming agent in the material. Therefore, it is not preferable.

  As the foaming agent and the carrier resin, a powder mixing device such as a ribbon blender, a tumbler, a Henschel mixer, a super floater or the like is used. A mixer is used.

  If the amount of foaming agent added is approximately 10 parts by weight or more, the composition can be used as a master powder, and after mixing with a natural resin at a certain ratio, it can be subjected to foam molding.

  In addition to the resin composition containing the foaming agent and the resin composition containing the foaming agent, generally used plastic additives and fillers may be contained.

  Plastic additives mentioned here include antioxidants, UV absorbers, light stabilizers, lubricants, antistatic agents, flame retardants, colorants, etc., and plastic fillers mainly improve rigidity and heat resistance. Inorganic fillers are included.

Antioxidants consisting of phenolic, phosphorus, sulfur and lactones may be added alone or in combination to prevent thermal degradation during resin processing, and weather resistance is required for outdoor use. In this case, a benzophenone-based, salicylate-based, benzotriazole-based, cyanoacrylate-based or hindered amine-based compound may be used as an ultraviolet absorber or light stabilizer. As a lubricant used to impart lubricity at the time of kneading and molding, a polyolefin wax, a higher fatty acid metal salt or amide, or an ester compound may be added. The antistatic agent has an effect of reducing the surface resistance value of the molded product by adhering moisture in the air to the surface of the molded product in order to prevent dust from adhering to the molded product. Specifically, nonionic surfactants are suitably used, and it is also possible to use amine compounds, glycerides, and their composites, and in recent years, polymers based on polyamide elastomers as permanent antistatic agents. Flame retardants include mainly organic halogen compounds, more preferably combinations of aromatic bromine compounds and antimony trioxide, inorganic and organic phosphorus flame retardants, metal oxides such as those found in aluminum hydroxide and magnesium hydroxide Are preferably used. As the colorant, a dye or pigment used for coloring a thermoplastic resin, or a powder, paste, or pellet in which they are easily dispersed may be used. Examples of the inorganic filler include calcium carbonate, talc, precipitated barium sulfate, mica, kaolin clay, hydrotalcite, diatomaceous earth, and metal oxides such as magnesium oxide and aluminum oxide.

When these additives and fillers are in powder form, it is effective to add them to the resin composition containing the foaming agent described in this report. The method of adding them is effective.
Examples and comparative examples are described below. The contents are shown in Table 1.

Carbonate having an average particle diameter of 0.03 mm measured by the same method as a foaming agent for 100 parts by weight of a pulverized polypropylene resin having an average particle diameter of 0.4 mm measured by a laser diffraction scattering method as a carrier resin. 10 parts by weight of sodium hydride was charged in 2 kg with a Henschel mixer (Henschel mixer FM100, volume produced by Mitsui Mining Co., Ltd. = 9 L), and the blade rotation speed was 3000 r. p. m. Was mixed for 10 minutes to obtain a resin composition for foam molding as a master powder.
Further, 10 parts by weight of this composition was added to and mixed with 100 parts by weight of the above pulverized polypropylene resin, and mixed with an injection molding machine with a clamping pressure of 75 t (IS-75E manufactured by Toshiba Machine Co., Ltd.) at a cylinder temperature of 210 ° C. A mold of × 100 cm × 3 cm was loaded and injection molding was performed. The injection molding was performed for 10 shots, and the expansion ratio (original density of the polypropylene resin / density of the foam molded product) and the foam layer of the cross section of the molded product were observed.

 [Comparative Example 1-1] 5 parts by weight of the same foaming agent used in Example 1 was similarly used in the Henschel mixer used in Example 1 for 100 parts by weight of the polypropylene resin (not crushed) used in Example 1. It mixed on condition and was set as the resin composition for foam molding. The obtained foam molding resin composition was evaluated in the same manner as in Example 1.

 [Comparative Example 1-2] After melt-kneading the foam molding resin composition prepared in Comparative Example 1-1 with a single-screw extruder having a cylinder temperature of 180 ° C. and L / D28, a strand having a diameter of 3 mm was drawn from the die, After cooling in a water tank, pellets having a diameter of 3 mm and a length of 3 mm were prepared with a rotary cutter. However, the above pellets have already started to be foamed and could not be used for foam molding.

  [Comparative Example 1-3] 5 parts by weight of the blowing agent used in Example 1 was mixed with 100 parts by weight of the ethylene-vinyl acetate copolymer as a carrier resin, and the extruder used in Comparative Example 1-2 was used. A foam molding resin composition was prepared by pelletizing at a cylinder temperature of 100 ° C. in the same manner as in Comparative Example 1-2. The obtained foam molding resin composition was evaluated in the same manner as in Example 1.

  As a carrier resin, 0.5 parts by weight of the foaming agent used in Example 1 was used in Example 1 for 100 parts by weight of a pulverized polystyrene resin having an average particle diameter of 0.45 mm measured in the same manner as in Example 1. With a similar device, blade rotation speed = 3000 r. p. m. Was mixed for 15 minutes to obtain a resin composition for foam molding. The obtained foam molding resin composition was evaluated in the same manner as in Example 1.

  [Comparative Example 2-1] 5 parts by weight of the same foaming agent used in Example 1 was similarly used in the Henschel mixer used in Example 2 for 100 parts by weight of the polystyrene resin (not crushed) used in Example 2. It mixed on condition and was set as the resin composition for foam molding. The obtained foam molding resin composition was evaluated in the same manner as in Example 1.

[Comparative Example 2-2] The foam molding resin composition prepared in Comparative Example 2-1 was melt-kneaded in a single-screw extruder with a cylinder temperature of 10 ° C. and L / D28, and then a strand with a diameter of 3 mm was drawn from the die. After cooling in a water tank, pellets having a diameter of 3 mm and a length of 3 mm were prepared with a rotary cutter. However, as in Comparative Example 1-2, the above pellets had already started to foam and could not be subjected to foam molding.

 [Comparative Example 2-3] The foam molding resin composition prepared in Comparative Example 1-3 was evaluated in the same manner as in Example 1.

実施例１、２ではショット間の発泡倍率のばらつきのない成形品が得られ
且つ微細で均一な発泡セルが成形品断面より確認された。

In Examples 1 and 2, a molded product having no variation in the expansion ratio between shots was obtained, and a fine and uniform foam cell was confirmed from the cross section of the molded product.

Claims (3)

To melt 0.1 to 50 parts by weight of an inorganic foaming agent having an average particle diameter of 001 to 0.1 mm with respect to 100 parts by weight of a thermoplastic resin having an average particle diameter of 0.01 to 1.0 mm. A resin composition for foam molding obtained by dispersing and mixing. The resin composition for foam molding according to claim 1, wherein the inorganic foaming agent is a carbonate. A foam molded article obtained by blending the resin composition of claim 1 or 2 with a thermoplastic resin and melt-molding it.